diavox courier 700, digital system telephone for md 110 data

97
Fig. 14
Line terminal rack for a system in the N2 construction
practice. Dimensions: height 2 600 mm,
width 120 mm and depth 225 mm. The right-hand
rack can be equipped with two remote power
feeding units
Fig. 15
The trial route near Stockholm
system housing in a polystyrene insert.
The repeaters are connected to the cable
terminals via flexible cables.
The repeaters should be insulated from
earth if there is large hum induction in
the cable. In such cases all metal parts
in the housing are, for safety reasons,
automatically earthed when the lid is
opened.
The housing also holds the fault detector
unit and a connector for connecting
a service telephone to the service circuit.
Fault location
Faulty intermediate repeaters are located
with the aid of the same system as
is used in the 2 Mbit/s and 8 Mbit/s line
systems 5 . The terminal equipments are
identical, which makes it possible to
connect the transmission maintenance
system ZAN 01.
The fault detector system allows detection
of bit errors in the line signal during
traffic by using the redundancy in the
line code. Each intermediate repeater
contains a fault detector circuit, which
is connected to a common fault detector
unit. The unit is connected to the
fault detector shelf via a separate pair.
Information regarding the bit error rate
on a certain intermediate repeater output
can be transmitted to the fault detector
shelf for analysis by means of a
simple addressing procedure. The fault
is located by addressing consecutive
intermediate repeaters and comparing
the bit error rates. The system can be
tested by injecting code errors in the
line terminating magazine. The error injection
will not interfere with the traffic,
since the errors are corrected in the
terminal equipment by means of the
redundancy in the code.
Locating a cable break
In the case of a cable break all power to
the dependent repeaters is immediately
cut off and the signal disappears, which
makes it impossible to locate the break
by means of the fault detector system.
In order to find the break the current
from the remote power feeding unit is
measured. The unit will be providing a
constant output voltage of 600 V 4 . Each
repeater contains a high-impedance resistor
between the two directions of
transmision, which gives a leakage current
of a certain value. During the installation
a calibration is carried out,
which provides a reference list of the
leakage readings for the individual repeaters.
Service telephone circuit
When ZAY 140-1 is used in the longdistance
network a 4-wire service telephone
circuit is often necessary because
of the long distances. At the terminals
the 4-wire service circuit equipment
is connected to the ordinary 2-
wire service telephone in the M5/BYB
rack. The permitted attenuation on the
loaded service circuit pair may be up to
about 40 dB.
FATME terminal equipment
FATME has developed a version of line
system ZAY 140-1 which has been designated
ZAYF 140, and which meets the
special Italian requirements. The main
difference is that the narrow rack in the
N2 construction practice has been used
for the line terminal, which takes up two
racks, fig. 14.
One of the racks holds the terminal repeaters
(top) and the line terminating,
fault detector and power feeding equipment.
The fault location system is similar
to that in ZAY 140-1. A micropro-